public class MyLinkedList implements IList{
    // 2、无头双向链表实现
    static class ListNode {
        public int val;
        public ListNode prev;
        public ListNode next;
        public ListNode(int val) {
            this.val=val;
        }

    }
        public ListNode head;
        public ListNode last;
        //头插法
        public void addFirst(int data){
            ListNode node=new ListNode(data);
            if(this.head==null) {
                this.head=node;
                this.last=node;
                return;
            }
            node.next=this.head;
            this.head.prev=node;
            this.head=node;
        }

        //尾插法
        public void addLast(int data){
            ListNode node=new ListNode(data);
            if(this.head==null) {
                this.head=node;
                this.last=node;
                return;
            }
            this.last.next=node;
            node.prev=this.last;
            this.last=node;
        }

        //任意位置插入,第一个数据节点为0号下标
        public void addIndex(int index,int data)throws Poslllegal{
            if(index==0) {
              addFirst(data);
              return;
            }
            int size=size();
            if(index==size) {
                addLast(data);
                return;
            }
            if(index<=0||index>size) {
                System.out.println("下标输入错误");
                throw new Poslllegal("插入下标元素异常:"+index);
            }
            ListNode node=new ListNode(data);
            ListNode cur=findIndex(index);
            node.next=cur;
            node.prev=cur.prev;
            cur.prev.next=node;
            cur.prev=node;
        }

        private ListNode findIndex(int index) {
            ListNode cur=this.head;
            while (index!=0) {
                cur=cur.next;
                index--;
            }
            return cur;
        }

        //查找是否包含关键字key是否在单链表当中
        public boolean contains(int key){
            ListNode cur=head;
            while (cur!=null) {
                if(cur.val==key) {
                    return true;
                }
                cur=cur.next;
            }
            return false;
        }

        //删除第一次出现关键字为key的节点
        public void remove(int key) {
            ListNode cur=this.head;
            while (cur!=null) {
                if(cur.val==key) {
                    if (cur==head) {
                        head=head.next;
                        if (head!=null) {
                            head.prev = null;
                        }
                    }else {
                        cur.prev.next=cur.next;
                        if (cur.next==null) {
                            last=last.prev;
                        }else {
                            cur.next.prev = cur.prev;
                        }
                    }
                    return;
                }
                cur=cur.next;
            }
        }



        //删除所有值为key的节点
        public void removeAllKey(int key){
            ListNode cur=this.head;
            while (cur!=null) {
                if(cur.val==key) {
                    if (cur==head) {
                        head=head.next;
                        if (head!=null) {
                            head.prev = null;
                        }
                        last=null;
                    }else {
                        cur.prev.next=cur.next;
                        if (cur.next==null) {
                            last=last.prev;
                        }else {
                            cur.next.prev = cur.prev;
                        }
                    }
                }
                cur=cur.next;
            }
        }

        //得到单链表的长度
        public int size(){
            int count=0;
            ListNode cur=this.head;
            while (cur!=null) {
                cur=cur.next;
                count++;
            }
            return count;
        }

        public void display(){
            ListNode cur=this.head;
            while (cur!=null) {
                System.out.print(cur.val+" ");
                cur=cur.next;
            }
        }

        public void clear() {
            ListNode cur=this.head;
            if (this.head.next==null) {
                this.head=null;
                this.last=null;
            }
            while (cur!=null) {
                ListNode node=cur.next;
                cur.prev=null;
                cur.next=null;
                cur=node;
            }
            this.head=null;
            this.last=null;
        }
    }
